du -xhd1 | sort -h // to directory sizes in the current directory
sed -i 's/foo/bar/g' * // Occurrences of "foo" in all files in cwd will be replaced with "bar".
for f in `find . -iname '*.oldext' -type f -print`;do mv "$f" ${f%.oldext}.newext; done // Change the extension of multiple files
grep -rnw '/path/to/somewhere/' -e 'pattern'
// -r or -R is recursive,
// -n is line number, and
// -w stands for match the whole word.
// -l (lower-case L) can be added to just give the file name of matching files.
// -e is the pattern used during the search

vimdiff <(xxd foo1.bin) <(xxd foo2.bin) // compare binary files

nload // monitor network
setxkbmap pl // set keyboard language to pl

iconv -f windows-1250 -t UTF-8 in.txt > out.txt // change file encoding

pulseaudio -k // repair Audio device got stuck!

watch -n.1 "grep \"^[c]pu MHz\" /proc/cpuinfo" // get cores frequency
cpupower frequency-set --governor powersave // set cpu frequency governor to min.
ps -e -o psr= | sort | uniq | wc -l // get working cores